1. Field of Invention
The present invention relates to a manufacture method of a transformer, and more particularly to a converter transformer with DC magnetic bias inhibition arrangement which is applicable for capacitance of different values.
2. Description of Related Arts
DC grid and geomagnetic variation are factors which increase a neutral ground point of a transformer, causing a DC bias current flowing into a coil of the transformer through the neutral and result in half-cycle saturation of magnetizing current of the transformer.
In the absence of DC current in a coil assembly of a transformer, no load current works in the linear segment of the iron-core magnetization curve Φ (t). At this point, the magnetizing current basically is a sine wave or approximately a sine wave which is symmetrical in shape, as shown by the solid line in FIG. 1(c). Under the influence of DC magnetic bias, which is shown in the broken line of FIG. 1(c), a shift is occurred to the exciting current under no-load condition in the iron-core magnetization curve Φ (t) in which the half wave works in the saturation zone, an elevated peak is occurred, and the sine wave is distorted to become asymmetrical from its originally symmetrical form.
Due to the half cycle saturation phenomenon which is occurred in the core, a large amount of saturated magnetic flux linkage forms a closed loop path outside the core, the exciting current is distorted dramatically, thereby the transformer itself will have increased wear and tear under no load condition and increased level of oscillation, increased noised level. In addition, the core, metal parts and oil tank of the transformer will become overheat while the insulation element will be damaged. When the situation is serious, the electric power system will be jeopardized and the power grid may be collapsed.